Much of my research has been geared towards hadron-collider efforts because this is the way to attain the highest energies needed to produce the heaviest particles. At the moment, the heaviest particle we know of is the top quark, and I have studied this particle for several years at the Fermilab Tevatron.

Top Physics

Quarks are currently understood to be among the most fundamental particles in nature. The majority of the observed matter in the universe is composed of subatomic protons and neutrons, which are in turn comprised of quarks. Although quarks were hypothesized 40 years ago, there remains considerable mystery about what determines the properties of these particles. These questions lie at the very foundation of physics. For instance, 'What is mass, and where does it come from?' Answering these questions is hampered by the fact that forces between quarks are so strong that it is virtually impossible to study each one in isolation. One quark, however, does not suffer from this problem: the top quark. Discovered in 1995, this particle has such unusual properties that it is currently viewed to hold important clues to the longstanding questions. One of these properties of the top quark is its mass.

Precisely measuring the top quark mass appears to tell us quite a bit about the way in which mass is 'created' at the level of fundamental physics. The ability to measure this mass well rests with the ability to use as many different 'channels' or final states for the measurement, as well as with excellent measurement of the energies of the 'daughter' particles top produces in the detector. I have been occupied with using dilepton events to pursue this measurement. These channels possess a complication in that they are missing key measurements that are used in other channels. By exploring the optimal ways that a mass measurement can be extracted from these events, and by using new dilepton channels for the mass measurement at D0 for the first time, a more precise measurement can be achieved. Most recently, this has resulted in new measurements of the top quark mass which are helping to understand the origin of mass. I have supported this work with calibration and monitoring efforts for LAr calorimeters at both D0 and ATLAS.

I have been studying the top quark for several years, dating back to my time as a graduate student on one of the teams that discovered this particle. If you are interested in some notes on what this work was like, here are two posters I recently gave as part of teh Top Turns Ten Symposium at Fermilab:

TopTurnsTen MainRing Poster

TopTurnsTen QuarkInTheLife Poster

Dark Matter

Observations of astrophysical processes have revealed the existence of a large preponderance of matter that is not visible and is of unknown type. Galactic rotational curves were early indicators of an excess of mass extending well beyond the luminous region. The pattern of inhomogeneity in the cosmic microwave background and red-shift measurements of distant supernovae constrain us to a cosmology which has an order of magnitude more matter than we can see or account for by Big Bang nucleosynthesis. Other cosmological studies, include that of large-scale structure formation, suggest a typical dark matter particle mass of order 1 TeV.

A wide range of supersymmetric (SUSY) models predicts particles that are massive, neutral but weakly interacting, and stable. The mass of these particles is inferred to be of order 1 TeV, placing them within the reach of the LHC.

Gamma-ray Bursts

Another avenue of research that I have pursued involves the study of high energy astrophysics events, particularly gamma-ray bursts. I have been a member in the ROTSE Experiment, which utilizes robotic telescopes to make fast optical measurements of these transient events. The first ROTSE telescope successfully observed for the first time optical emission coming from a burst while the brief gamma-ray emission was still occurring. This observation, further studies of gamma-ray burst triggers, and untriggered searches for optical bursts have shed light on these mysterious phenomena. It is currently believed that they arise from a sort-of massive supernova, or hypernova, that creates intense gamma-ray emission out the poles of the object. The fast optical emission is taken as evidence that the gamma-rays are being generated internally to the burst event, rather than in some external medium.